1. Field of the Invention
This invention relates to a non-magnetic substrate material to be used for floating-type magnetic head sliders for high frequency, high density storage magnetic disk units, and to a composite-type floating magnetic head (hereinafter sometimes called "Composite Type Head") and thin film-type floating magnetic head (hereinafter sometimes called "Thin Film Head") for which the abovementioned material is used.
2. Related Art
Magnetic disks have been used for 3.5", 2.5" and high density compact magnetic disk units and are available in two types, the composite type head disk unit which is shown in FIG. 1 and currently the most popular, and the thin film head type disk unit which is shown in FIG. 2 and which is likely to be increasingly used as further advances are made in densification.
In FIG. 1, element 11 is the composite-type floating magnetic head and element 12 is a slider composed of non-magnetic materials, such as ceramics. A magnetic head core 13 is fixed and retained in a slit 14 formed in an air bearing 16 with molded glass 15.
FIG. 4 is a perspective view showing magnetic head core 31, generally referred to in FIG. 1 as element 13. The magnetic head core 31 consists of a pair of facing core blocks 32 and 33, having a magnetic gap 37 between them. Soft magnetic alloy thin films 35 and 36, are formed by sputtering on both core blocks and are reinforced with glass 34 for adhesion.
The above magnetic head core is generally made of Mn--Zn single crystal ferrite with a thermal expansion coefficient of about 110.times.10.sup.-7 /.degree. C. The magnetic head core is set in the slider slit and fixed with glass as discussed above with reference to FIG. 1. Thus, if the thermal expansion coefficient is substantially different from that of the slider, the glass will be easily cracked. Consequently, it is necessary to approximate the thermal expansion coefficient of the magnetic head core to that of the slider.
A non-magnetic substrate material suitable for such composite-type sliders is one composed of a TiO.sub.2 --BaO--CaO component, such as disclosed in Japanese Patent Laid-Open Publication No. 243562/1990, along with at least one additive of Al.sub.2 O.sub.3, NiO, SrO, MgO, Y.sub.2 O.sub.3, WO, MoO.sub.3, In.sub.2 O.sub.3 and ZrO.sub.2. The thermal expansion coefficient of this non-magnetic substrate material is about 115.times.10.sup.-7 /.degree. C., which is close to that of Mn--Zn ferrite for the magnetic head core. The additive, such as Al.sub.2 O.sub.3, makes a finer crystal grain, reduces gaps between crystal grains and makes them uniform. Thus, this non-magnetic substrate material can be easily machined with substantially reduced chipping and is regarded as a superior material for this type of application.
FIG. 2 is a perspective view showing a thin film-type magnetic head as an example, wherein element 20 is a magnetic head, 21 element is an air bearing, element 22 is an electromagnetic converter and element 23 is a slider. The electromagnetic converter generally forms Al.sub.2 O.sub.3 film on the ends of the non-magnetic slider and also forms amorphous or other thin film on it according to lithographic thin-film technology. Therefore, from the aspects of manufacture and operation, it is necessary to retain a proper relationship between their thermal expansion coefficients. The slider is generally made of a substrate material composed principally of alumina-titanium carbide (ATC).
To ensure that the quality of magnetic disk units corresponds to that of modern high-density recording, hard disks, as magnetic recording media, feature disk boards onto which the magnetic substance is closely adhered by plating or sputtering techniques.
The surfaces of the abovementioned disk boards finished by plating or sputtering are of a higher level of accuracy than those finished by conventional painting. However, since lubricant is coated over the surface, an unprecedented problem known as a sticking phenomenon occurs between the head and disk surfaces. In other words, when the surface accuracy of a plane opposite a magnetic recording medium is improved, the stationary disk surface and head surface opposite the disk stick together. If the adhesive strength between the head and disk increases excessively, it will exceed the torque of the motor which rotates the disk. Consequently, operation of the disk unit is drastically impaired. At the same time, CSS (Contact Start and Stop) life is shortened. This constitutes a serious problem for small magnetic disks which require a flying height of less than 0.1 .mu.m.
To improve the CSS property, various studies have also been carried out on magnetic disks which are processed by a texture. Texture process is a process whereby numerous irregularities are formed on the disk board, where average surface roughness is about 10 nm and pitch between peaks and valleys of irregularities is 100 to 200 nm, as indicated in FIGS. 3A and 3B measured in the radial direction of the disk by HIPOSS (Tracer-type minute shape measuring instrument). After the texture process, the disk board is covered with a primer film of Cr, then with metallic magnetic thin film of Co--Cr--Ta, etc. by sputtering and is finally protected with carbon film. These irregularities processed by the texture, reduce contact area between the magnetic head and the air bearing face and provide appropriate adhesive strength.
On the other hand, the non-magnetic substrate material to be used for the slider of the composite type head is made of the TiO.sub.2 --BaO--CaO component and at least one additive of Al.sub.2 O.sub.3, NiO, SrO, MgO, Y.sub.2 O.sub.3, WO, MoO.sub.3, In.sub.2 O.sub.3 and ZrO.sub.2 and is suitable for the slider in terms of thermal expansion coefficient and processability. However, its Vickers hardness is about 850 Kg/mm.sup.2 which is higher than that of the disk processed by texture. The magnetic head slides the protective film at flying and landing, and the peak sections of the disk irregularities processed by texture are to be partly damaged.
Also, alumina-titanium carbide to be used for the substrate which forms the slider of the thin film head causes problems with lubrication of disk or recording medium, due to titanium carbide being active, and is more uncongenial to a disk than TiO.sub.2 --BaO--CaO non-magnetic substrate material because the Vickers hardness is as high as 2,000 Kg/mm.sup.2, and has problems in regard to its processability.